Sodium cyanate

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

3. ANALOGUE APPROACH JUSTIFICATION
Read across from potassium cyanate was performed. No major differences in hydrolysis are to be expected based on the structure of the molecules. Furthermore, data on hydrolysis of the target substance itself are also available confirming this assumption.

Reason / purpose for cross-reference:

read-across source

Transformation products:

not measured

% Recovery:

53

pH:

9

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other: no detailes data provided

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1956

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Public available literature (no Guideline, no GLP)

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Public available literature. No guideline indicated. For details on method see materials and methods section.

GLP compliance:

not specified

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
not indicated.

Radiolabelling:

not specified

Analytical monitoring:

not specified

Details on sampling:

not indicated.

Buffers:

not indicated.

Estimation method (if used):

not indicated.

Details on test conditions:

not indicated.

Number of replicates:

not indicated.

Positive controls:

not specified

Negative controls:

not specified

Statistical methods:

not indicated.

Preliminary study:

not indicated.

Test performance:

not indicated.

Transformation products:

yes

No.:

#1

No.:

#2

Details on hydrolysis and appearance of transformation product(s):

Simultaneous formation of urea and carbonate from aqueous solutions of sodium cyanate at ca. 60° C and 80° C.
NCO- + 2H2O => CO3 2- + NH4+
NCO- + NH4+ => CO(NH2)2

Remarks on result:

other: no detailed data provided

Remarks on result:

other: no detailed data provided

Other kinetic parameters:

not indicated.

Details on results:

not indicated.

Validity criteria fulfilled:

not specified

Conclusions:

Simultaneous formation of urea and carbonate from aqueous solutions of sodium cyanate at ca. 60° C and 80° C. The reaction can be expressed by the following formulas:
NCO- + 2H2O => CO3 2- + NH4+
NCO- + NH4+ => CO(NH2)2

Reference 3

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

from 2008-12-02 to 2009-06-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Water solubility (IUCLID5 section 4.8)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
water solubility: 96.4 g/L

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Samples were taken and measured after 2, 4, 7.5, 24 and 30 hours and on days 4, 5, 6 and 7 in order to collect information about the kinetics of hydrolysis.
1.0 mL of the diluted sample was mixed with 1.0 mL of 0.02-molar anthranilic acid and kept at 40 °C for 10 minutes. Then, 2 mL HCl 37% were added, the solution was heated to 100 °C for 1 minute and then left to cool down to room temperature.

Buffers:

Deionised water (conductivity below 0.1 S/cm and TOC below 5 ppm) was used for the test (commercially available doubly distilled water guarantees conductivity as large as 5 µS/cm).

Estimation method (if used):

NA

Details on test conditions:

In a water solubility study also hydrolysis was observed and recorded at 20°C.

Duration:

7 d

Temp.:

20 °C

Initial conc. measured:

97.06 mg/L

Number of replicates:

2 Experiments with different sampling times (one sample each).

Positive controls:

no

Negative controls:

no

Statistical methods:

NA

Preliminary study:

NA

Test performance:

NA

Transformation products:

yes

No.:

#1

Details on hydrolysis and appearance of transformation product(s):

Qualitative analysis of the remaining solution showed presence of ammonia, which could not be detected in a freshly prepared solution of the test item. Literature also describes hydrolysis of cyanates to ammonia and carbon dioxide with time.

Key result

pH:

10

Temp.:

20 °C

DT50:

7 d

Type:

not specified

Other kinetic parameters:

Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20°C. This DT50 corresponds to 13 days at 12°C.

Day	Absorption diluted sample	Concentration in flask	Difference to previous sample	pH
#	310 nm	g/L	%	---
3	0.93045	90.6	---	approx. 10
4	0.79955	78.0	-14.0	approx. 10
5	0.69131	67.5	-13.4	approx. 10
6	0.57957	56.7	-16.0	approx. 10
7	0.47523	46.6	-17.8	approx. 10

 

Validity criteria fulfilled:

not applicable

Conclusions:

Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20°C. This DT50 corresponds to 13 days at 12°C.

Executive summary:

In a water solubility study also hydrolysis was observed and recorded at 20°C. Samples were taken and measured after 2, 4, 7.5, 24 and 30 hours and on days 4, 5, 6 and 7 in order to collect information about the kinetics of hydrolysis. Qualitative analysis of the solution showed presence of ammonia, which could not be detected in a freshly prepared solution of the test item. Literature also describes hydrolysis of cyanates to ammonia and carbon dioxide with time. Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20°C. This DT50 corresponds to 13 days at 12°C.

Reference 4

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

from 2009-12-11 to 2009-12-16

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

13 April 2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Version / remarks:

Regulation 440/2008

Deviations:

no

Principles of method if other than guideline:

NA

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
no details given

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Samples were diluted with buffer and water to fit the calibrated range. The pH value if the diluted samples was adjusted to pH 4.5. 2-aminobenzoic acid and then hydrochloric acid solution was added and the solution was thermostated.

Buffers:

All buffers were diluted with ultra-pure water and adjusted with 0.2 M sodium hydroxide.
pH 4.0: 0.2 M Potassium hydrogen phthalate
pH 7.0: 0.2 M Potassium dihydrogen phosphate
pH 9.0: 0.2 M Boric acid and potassium chloride

Details on test conditions:

Temperature: 50 °C +/- 0.5 °C
Light and oxygen: the reaction was carried out using a dark thermostat to avoid photolytic effects. Nitrogen was bubbled into the water for 5 minutes before the preparation of the solutions in order to exclude oxygen.

All glassware, water and buffer solutions were sterilised.

Duration:

5 d

pH:

4

Temp.:

50 °C

Initial conc. measured:

ca. 305 mg/L

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

ca. 381 mg/L

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

ca. 377 mg/L

Number of replicates:

five

Negative controls:

yes

Remarks:

control buffer

Statistical methods:

Calculation and construction of the calibration curves were carried out using "EXCEL for Windows".

Preliminary study:

The hydrolysis rate of the test item was found to be 47 % at pH 9 and approximately 100 % at pH 4 and 7. For the latter concentrations were below the detection limit after 5 days.

Transformation products:

not measured

% Recovery:

0

pH:

4

Temp.:

50 °C

Duration:

5 d

% Recovery:

0

pH:

7

Temp.:

50 °C

Duration:

5 d

% Recovery:

53

pH:

9

Temp.:

50 °C

Duration:

5 d

Remarks on result:

other: no detailed data provided

Analysis of Samples

The content of potassium cyanate in the different pH buffer samples was determined at the beginning and the end of hte test periods. Three samples were taken and analysed at the starf of the study. Five samples were taken from five separate tubes of the hydrolysis test and were anaylsed after 120 hours. Sample volume was 1 mL. This was diluted fivefold at the start of the study. At the end of the preliminary test the samples of buffer solution pH 9 were diluted fivefold. The samples of buffer solution pH 4 were analysed without dilution. The samples of buffer solution pH 7 were diluted twofold. One sample was taken from the control vessel anddiluted in the same way as the samples.

Measured data at a temperature of 50 °C at the start and after 120 hours

pH	Sampling time (hour)	Concentration of potassium cyanate  (mg/L )			Hydrolysis (%)	Measured pH
		Test vessels	Mean withthe 95% confidence intervals
4	Start	Control buffer			-	4.00
		293	305 ± 16.5		-	4.05
		316				4.05
		306				4.10
	120	Control buffer			-	4.05
		< LOQ	< LOQ		100	4.42
		< LOQ				4.44
		< LOQ				4.42
		< LOQ				4.44
		< LOQ				4.40
7	Start	Control buffer			-	7.00
		372	381 ± 10.9		-	7.02
		383				7.02
		387				7.03
	120	Control buffer			-	7.04
		< LOQ	< LOQ		100	7.25
		< LOQ				7.30
		< LOQ				7.28
		< LOQ				7.30
		< LOQ				7.25
9	Start	Control buffer			-	9.00
		390	377 ± 33.1		-	8.98
		391				8.98
		351				8.99
	120	Control buffer			-	8.98
		198		198 ± 2.3	47	9.01
		204				9.03
		197				9.02
		201				9.02
		193				9.03

 

Validity criteria fulfilled:

yes

Conclusions:

Based on the results of the preliminary test the hydrolysis rate of potassium cyanate was found to be 47 % at pH 9 after 5 days at 50 °C. Hydrolysis rates at pH 4 and pH 7 were approximately 100 %.

Executive summary:

Purpose

The purpose of this study was to evaluate the hydrolysis of potassium cyanate in different pH buffer solutions.

Results:

Based on the results of the preliminary test the hydrolysis rate of potassium cyanate was found to be 47 % at pH 9 after 5 days at 50 °C. Hydrolysis rates at pH 4 and pH 7 were approximately 100 %.

Reference 5

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1958

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: public available literature (non GLP, non guideline)

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Public available literature. No guideline indicated. For details on method see materials and methods section.

GLP compliance:

not specified

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
not indicated.

Radiolabelling:

not specified

Analytical monitoring:

not specified

Details on sampling:

not indicated.

Buffers:

not indicated.

Estimation method (if used):

not applicable.

Details on test conditions:

Aerobic decomposition studies:
Cyanate stability was studied at room temperature in solutions buffered at pH values of 3.1, 4.0, 4.6, 5.0 and 5.5. A pH of 5.0 was used for studies conducted at 5°C.

Number of replicates:

not indicated.

Positive controls:

not specified

Negative controls:

not specified

Statistical methods:

not indicated.

Preliminary study:

not indicated.

Test performance:

not indicated.

Transformation products:

not specified

Details on hydrolysis and appearance of transformation product(s):

not indicated.

pH:

5

Temp.:

25 °C

Hydrolysis rate constant:

1.8 h-1

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: aerobic decomposition

Other kinetic parameters:

not indicated.

Details on results:

Aerobic decomposition studies:
The rate of decomposition with respect to the cyanate ion shows an apparent first order reaction.
Cyanate persistance was further studied in unbuffered sulfuric acid solutions at initial pH values of 4.2, 4.7 and 5.5. Cyanate stability was also observed in distilled water initially at pH 6.8 and in river water samples taken from Ohio and the Big and Little Miami Rivers. In the temperature range studied, at a pH equal to or greater than 7.2 the cyanate ion is very stable and at room temperatures, cyanate solutions have remained stable more than 4 weeks.

Validity criteria fulfilled:

not specified

Conclusions:

The rate of decomposition with respect to the cyanate ion shows an apparent first order reaction. In the temperature range studied, at a pH equal to or greater than 7.2 the cyanate ion is very stable and at room temperatures, cyanate solutions have remained stable more than 4 weeks.

Executive summary:

Cyanate stability was studied at room temperature in solutions buffered at pH values of 3.1, 4.0, 4.6, 5.0 and 5.5. A pH of 5.0 was used for studies conducted at 5°C. The rate of decomposition with respect to the cyanate ion shows an apparent first order reaction.

Cyanate persistance was further studied in unbuffered sulfuric acid solutions at initial pH values of 4.2, 4.7 and 5.5. Cyanate stability was also observed in distilled water initially at pH 6.8 and in river water samples taken from Ohio and the Big and Little Miami Rivers. In the temperature range studied, at a pH equal to or greater than 7.2 the cyanate ion is very stable and at room temperatures, cyanate solutions have remained stable more than 4 weeks.

Reference 6

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1989

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Public available literature. No guideline indicated. For details on method see materials and methods section.

GLP compliance:

not specified

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
not indicated.

Radiolabelling:

no

Analytical monitoring:

not specified

Details on sampling:

not indicated.

Buffers:

not indicated.

Estimation method (if used):

not applicable.

Details on test conditions:

not indicated.

Number of replicates:

not indicated.

Positive controls:

not specified

Negative controls:

not specified

Statistical methods:

not indicated.

Preliminary study:

not indicated.

Test performance:

not indicated.

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on hydrolysis and appearance of transformation product(s):

Cyanates are stable in aerobic water at pH 7 and 20°C for at least 10 days, eventually undergoing hydrolysis to yield ammonium carbonate. In anaerobic solution, cyanates are reduced to a mixture of ammonia and formic acid.

Remarks on result:

other: no detailed data provided

Key result

pH:

7

Temp.:

20 °C

DT50:

> 10 d

Remarks on result:

other: no detailed data provided

Other kinetic parameters:

not indicated.

Details on results:

not indicated.

Validity criteria fulfilled:

not specified

Conclusions:

Cyanates are stable in aerobic water at pH 7 and 20°C for at least 10 days, eventually undergoing hydrolysis to yield ammonium carbonate. In anaerobic solution, cyanates are reduced to a mixture of ammonia and formic acid.

Reference 7

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1983

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Public available literature. No guideline indicated. For details on method see materials and methods section.

GLP compliance:

not specified

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
not indicated.

Radiolabelling:

no

Analytical monitoring:

not specified

Details on sampling:

not indicated.

Buffers:

not indicated.

Estimation method (if used):

not indicated.

Details on test conditions:

not indicated.

Number of replicates:

not indicated.

Positive controls:

not specified

Negative controls:

not specified

Statistical methods:

not indicated.

Preliminary study:

not indicated.

Test performance:

not indicated.

Transformation products:

yes

No.:

#1

No.:

#2

Details on hydrolysis and appearance of transformation product(s):

Sodium cyanate is soluble in water and decomposes to form sodium carbonate and urea.

Remarks on result:

other: no detailed data provided

Remarks on result:

other: no detailed data provided

Other kinetic parameters:

not indicated.

Details on results:

not indicated.

Validity criteria fulfilled:

not specified

Conclusions:

Sodium cyanate is soluble in water and decomposes to form sodium carbonate and urea.

Description of key information

From a water solubility study with sodium cyanate a DT50 of 13 d at 12 °C could be extrapolated. This value is used as worst case value in the risk assessment.

Key value for chemical safety assessment

Half-life for hydrolysis:

13 d

at the temperature of:

12 °C

Additional information

 

In a water solubility study also hydrolysis was observed and recorded at 20°C. Samples were taken and measured after 2, 4, 7.5, 24 and 30 hours and on days 4, 5, 6 and 7 in order to collect information about the kinetics of hydrolysis. Qualitative analysis of the solution showed presence of ammonia, which could not be detected in a freshly prepared solution of the test item. Literature also describes hydrolysis of cyanates to ammonia and carbon dioxide with time. Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20°C. This DT50 corresponds to 13 days at 12°C.

The further available hydrolysis studies conducted with sodium cyanate show different results depending on the test conditions used. In a state of the art guideline study with the structural analogue potassium cyanate hydrolysis of cyanates was evaluated. Thus, read across from potassium cyanate was performed. It is not expected that the different cyanates behave differently regarding their hydrolysis behaviour.

In this study the hydrolysis of potassium cyanate in different pH buffer solutions was evaluated in a preliminary screening test. Based on the results of the preliminary test the hydrolysis rate of potassium cyanate was found to be 47 % at pH 9 after 5 days at 50 °C. Hydrolysis rates at pH 4 and pH 7 were approximately 100 %.

 

Further studies:

- In a water solubility study with sodium cyanate also hydrolysis was observed and recorded at 20°C. Samples were taken and measured after 2, 4, 7.5, 24 and 30 hours and on days 4, 5, 6 and 7 in order to collect information about the kinetics of hydrolysis. Qualitative analysis of the solution showed presence of ammonia, which could not be detected in a freshly prepared solution of the test item. Literature also describes hydrolysis of cyanates to ammonia and carbon dioxide with time. Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20°C. This DT50 corresponds to 13 days at 12°C. Taking all available data together a worst case DT50 of 13 d at 12°C could be concluded.

- Cyanates are stable in aerobic water at pH 7 and 20°C for at least 10 days, eventually undergoing hydrolysis to yield ammonium carbonate. In anaerobic solution, cyanates are reduced to a mixture of ammonia and formic acid.

- Sodium cyanate is soluble in water and decomposes to form sodium carbonate and urea.

- Simultaneous formation of urea and carbonate from aqueous solutions of sodium cyanate at ca. 60° C and 80° C. The reaction can be expressed by the following formulas:

NCO-+ 2 H2O => CO32-+ NH4+

NCO-+ NH4+ => CO(NH2)2

- Cyanate stability was studied at room temperature in solutions buffered at pH values of 3.1, 4.0, 4.6, 5.0 and 5.5. A pH of 5.0 was used for studies conducted at 5°C. The rate of decomposition with respect to the cyanate ion shows an apparent first order reaction.

Cyanate persistance was further studied in unbuffered sulfuric acid solutions at initial pH values of 4.2, 4.7 and 5.5. Cyanate stability was also observed in distilled water initially at pH 6.8 and in river water samples taken fromand the Big and Little Miami Rivers. In the temperature range studied, at a pH equal to or greater than 7.2 the cyanate ion is very stable and at room temperatures, cyanate solutions have remained stable more than 4 weeks.